Proforma Invoice- multi lined SO

Is it not possible to create a proforma invoice for each sales order line?  I tried to pull in the SO from the PRO invoice transaction but the SO is not being displayed.  When I create the proforma from the SO function, all the lines display.  We are looking to create a proforma invoice for each line (as there are different dely dates for each line).   

Any help is  appreciated.

C